High current electrical contact arrangement

ABSTRACT

An electrical contact arrangement is provided for an electrical machine such as a unipolar machine or the like equipped with a ring-shaped rotatable member and a stationary member adjacent the rotatable member. The electrical contact arrangement includes first and second surfaces which are formed on the members, respectively, and which are mutually adjacent to conjointly define an annular gap having an approximate uniform thickness about its periphery. A liquid conductor supply communicates with the gap for supplying a liquid conductor under pressure to completely fill the gap thereby establishing a good electrical contact between the members about the periphery of the gap.

United State-s Patent [1 1 Massar Oct. 28, 1975 HIGH CURRENT ELECTRICAL CONTACT ARRANGEMENT [75] Inventor: Ernst Massar, Erlangen, Germany [22] Filed: Mar. 15, 1974 [21] Appl. No.: 451,496

[30] Foreign Application Priority Data OTHER PUBLlCATIONS Electrotechnik und Maschinenbau, 1972, p. 442, Fig.

Electrotechnik undMaschinenbau, 1961, pp. 132 and 133.

Primary ExaminerRobert K. Schaefer Assistant ExaminerM. Ginsburg Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT An electrical contact arrangement is provided for an electrical machine such as a unipolar machine or the like equipped with a ring-shaped rotatable member and a stationary member adjacent the rotatable member. The electrical contact arrangement includes first and second surfaces which are formed on the members, respectively, and which are mutually adjacent to conjointly define an annular gap having an approximate uniform thickness about its periphery. A liquid conductor supply communicates with the gap for supplying a liquid conductor under pressure to completely fill the gap thereby establishing a good electrical contact between the members about the periphery of the gap.

5 Claims, 3 Drawing Figures US. Patent Oct. 28, 1975 Fig. 3

Fig. 2

HIGH CURRENT ELECTRICAL CONTACT ARRANGEMENT BACKGROUND OF THE INVENTION The invention relates to an electric contact arrangement for high-currents wherein a liquid conductor provides an electrical contact between stationary and rotatable members.

Brushes are usually used for taking current from rotating, annular parts, which, however, are subject to wear and require continuous maintenance. It is known to use liquid contacts instead of brushes. In the liquid contacts, the electrical connection between the rotating and the stationary parts is established through a metallic liquid, that is, a liquid metal. However, relatively high friction losses are produced with such contacts and efforts have been made to reduce such losses, for example, by keeping the contact areas of the liquid metal small.

Reference may be had to the journal, Elektrotec/mik und Maschinenbau, 1972, page 442, particularly FIG. 8, wherein a liquid contact usable for large unipolar machines which operates according to the jet principle is described. Here, a metallic liquid under pressure is forced into the gap between the two annular parts by means of a jet. However, this jet results in a narrow gap between the stationary and the rotating part only at one, locally very constricted point, where the liquid emerging under pressure establishes the contact.

It has been found that the metallic liquid, which is greatly accelerated at this contact point, is finely atomized upon impact on the opposite walls of the stationary part and is readily oxidized, which makes it difficult to return the collected metal to the liquid contact in a closed circuit. In addition, the liquid contact provided at only one point on the circumference of the rotating annular part has the further disadvantage that the currents which are uniformly distributed along the circumference of the rotating annular disc must be conducted through this point contact, and large voltage drops are caused thereby. Compensating 'the current pattern caused thereby by opposite current loading in a further stationary annular disc, arranged parallel to the rotating annular disc, is possible only to a degree that can be described as imperfect.

SUMMARY OF THE INVENTION It is an object of the invention to provide a liquid contact arrangement which overcomes the disadvantages referred to above. It is also an object of the invention to provide a liquid contact arrangement wherein a uniform current distribution is achieved in the ringshaped members of the arrangement and wherein compensation is thereby easily achieved without having friction losses which are too high.

The contact arrangement of the invention is based on an electrical contact device for large currents, particularly in an electric unipolar machine, consisting of a liquid contact between a rotating annular part and an opposite, likewise annular, stationary part, in which the metallic liquid is forced under pressure into the gap between the two annular parts. According to the invention, the annular gap between the two parts has approximately the same thickness along the circumference and is completely filled by the metallic liquid under pressure. This metallic liquid under pressure thus forms a closed, pressurized film in the ring gap between the rotating and the stationary part. This action is analagous to that associated with the ring gaps of pressurized oil bearings. A reliable contact is thereby established between the two parts over the entire circumference. A very uniform current distribution within the ring discs results so as to afford a ready possibility to compensate the magnetic field produced by the current. The voltage drop is in the order of millivolts with this kind of Contact, so that high efficiency is obtained in conjunction with the low friction losses that are attainable by a suitable choice of the liquid metal alloys used. The liquid contact according to the invention affords the further advantage that it is independent of the direction of rotation of the rotating part and can therefore be used particularly in machines with variable speed and also with reversible direction of rotation, as such changes do not destroy the current-transmitting film in the annular gap. Thus, a liquid contact of this type is particularly well suited for application in unipolar machines used as a motor.

For supplying the metallic liquid, it is advisable to provide a ring canal in the vicinity of the annular gap. It is preferable to provide the ring canal in the stationary part. However, one can also provide, instead of one continuous ring canal along the circumference of the annular stationary part, several successive ring canal sections, each of which has its own supply of liquid metal. In this case the distance between the ring portions connecting the ring canal sections with each other and the rotating part should not be chosen smaller than the thickness of the annular gap.

It is advantageous to make the ring gap two or several tenths of a millimeter thick. However, since also in the narrowest mechanically permissible ring gaps wherein the liquid metal film is generated in the liquid contact developed in accordance with the invention, turbulant flow occurs at higher circumferential velocities and the friction losses produced by them increase approximately with the third power of the relative velocity between the film-bounding walls, it is advisable to arrange, according to a further embodiment of the invention, an intermediate ring freely floating in the liquid in the annular gap. The intermediate ring is self-centering radially and axially and has at the center openings distributed over the circumference which serve to reduce the velocity difference. The liquid metal forced into the annular gap under pressure distributes itself largely unimpeded in the annular gaps above and below the intermediate ring. Thus, two contact-making liquid metal films are produced, which are electrically connected in series. The intermediate ring floats freely in the annular gap between the stationary and the rotating part and assumes a velocity of approximately one-half of that of the rotating part because of the approximately equal friction losses in the confining annular gaps. In this manner, a reduction of the velocity difference between the annular gap walls is achieved which confine the respective contact-makin g liquid metal films. The friction losses are thereby reduced.

It is thus possible, by using several intermediate rings arranged radially on top of each other, with a corresponding number of velocity gradations, to lower the friction losses to a particularly great extent, so that liquid contacts configured according to the invention can also be used with known liquid metals such as mercury or alloys of sodium and potassium or gallium and indium in high-speed generators with good efficiency.

Furthermore, several intermediate rings can also be arranged side by side in a ring gap.

The axial centering, that is, the lateral centering of the intermediate ring freely floating'in the liquid metal filling the annular gap can be accomplished in a simple manner by axial centering means in the form of radial projections facing the stationary part. Radial centering is accomplished automatically through the reduction of j the pressure in a partial ring gap that becomes larger and the corresponding increase of the pressure in the other partial ring gap on the other side of the ring during the motion of the intermediate ring.

Although the invention is illustrated and described herein as a high current electrical contact arrangement for electrical machines such as a unipolar machine and the like, it is nevertheless not intended to be limited to the details shown, since various modifications may be 1 made therein within the scope and the range of the claims. The invention, however, together with additional objects and advantages will be best understood from the following description and in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The electric unipolar machine shown in FIG. 1 can be used as a motor with variable speed and also with reversible direction of rotation, for example, as is required in the propulsion system of a ship. The machine essentially includes several ring-shaped discs 2 mounted on a shaftl so as to be insulated with respect thereto. The discs 2 rotate in the magnetic field produced by superconducting coils 3. This magnetic field induces in each rotating disc 2 a voltage which causes a current I to flow in a closed external circuit; in each case the current enters at the radially inner liquid contact 4 and flows out at the radially outer liquid contact 5. At these locations, each of the ring discs 2 is surrounded by adjacent, likewise annular stationary parts 6 and 7, respectively, in such a manner that the ring gap 8 is in each case formed in between. In the vicinity of the ring gap 8 is located in the stationary parts 6 and 7, approximately centrally arranged, a ring canal 9, to which the liquid metal or the liquid metal alloy is fed from suitable pressure tanks, not shown, through bores 10. While the bores 10 located at the outside diameter of the parts 7 for the liquid contacts 5 are easily accessible, the feeding at the bores of the radially inner liquid contacts 4 requires special means for conducting the liquid metal, for instance, insulated tubes 11, which are attached to the parts 7. I

The liquid contacts 4 and 5 are established by feeding liquid metal under pressure to the ring canal 9 through the bores 10. In this way a continuous liquid metal film is formed in the narrow ring gap 8, which has an approximately uniform thickness of about 0.2 mm along the circumference. The continuous liquid metal film is formed between the two walls bounding the ring gap 8 5 so that the ring gap 8 is completely filled by the metallic liquid under pressure. This produces a good contact between the rotating annular discs 2 and the stationary parts 6 and 7 along the entire circumference of the ring gap 8. For compensating the currents I flowing in the individual ring discs 2, the stationary parts 7 are likewise of ring-disc shape and are always disposed immediately next to a ring disc 2. The currents I of equal magnitude but opposite direction flowing in the stationary part 7 cancel the field of the radial currents in the rotating ring disc 2 and thereby prevent a reaction on the useful flux of the field produced by coils 3.

The liquid metal, which leaves or is thrown from the ring gap 8 at the liquid contacts 4 and 5 flows off in suitably formed canals 12 in the stationary parts 6 or 7, is collected in receptacles, not shown, and is returned by a pump to the pressure tank, from which the pressurized liquid metal is again supplied to the ring gap 8. It should be noted here that because of the electric series connection of the individual rotating ring discs 2, the liquid metal of the individual liquid contacts 4 and 5 has different potential so that the individual returns must be separated from each other. Only liquid metal of the same electric potential can be circulated by one pump, so that a corresponding number of pumps and pressure tanks must be provided, which are mounted so as to be insulated according to their different electric potentials. From there, the liquid metal is again fed to the respective ring gaps 8. In case of increased heating of the liquid metal because of the friction and electrical losses occurring within the liquid contact 4 or 5, it is advisable to provide a cooler in each of the individual returns wherein the liquid metal gives off the loss heat absorbed by it, so that an operating temperature as advantageous as possible can be maintained.

If the liquid metal used, such as, for instance, mercury, has toxic properties, or requires a moisture-free atmosphere as is required, for instance in the case of sodium-potassium, it is necessary and possible without difficulty to accommodate the arrangement in a housing which is closed off by a separate partition 13 and is filled with an inert gas, suchas nitrogen. In addition, between the partition 13 and the housing wall proper 14 of the unipolar machine a nitrogen atmosphere subjected to over pressure can further be provided to prevent the vapors of the liquid metal from passing into the ambient air.

FIG. 2 shows an embodiment of a liquid contact 4 or 5 constructed in accordance with the invention and is suited particularly for use in unipolar machines operating at high speed. Here, an intermediate ring 15 is arranged between the rotating ring disc 2 and the stationary part 7. This intermediate ring 15 has a reduced thickness at the center portion thereof and a large number of openings 16. The liquid metal supplied to the ring canal 9 under pressure through the bores 10 is thereby distributed uniformly and with low friction losses to the partial ring gap 17 above the intermediate ring 15 and the partial ring gap 18 below the intermediate ring 15. Both partial ring gaps 17 and 18 are electrically connected in series, and through the normal pressure equalization, the same thickness adjusts itself for both partial ring gaps. As the friction losses in the two partial ring gaps 17 and 18 are sufficiently equal in magnitude, the intermediate ring will assume a velocity which is approximately one-half of the velocity of the rotating ring disc 2. Radial projections 19 are provided at the outer edges facing the stationary part 7 for axially centering the intermediate ring 15. Because of the arrangement of an intermediate ring 15 between the rotating ring disc 2 and the stationary part 7 as well as because of the two partial ring gaps 17 and 18 provided thereby in the liquid contact 4 or 5 wherewith always half the relative velocity between the bounding walls is obtained, the friction losses drop to approximately one-quarter of the value of the losses which occur without intermediate ring 15 and where only one ring gap of about the same thickness is present.

FIG. 3 shows a different configuration of such an intermediate ring 15 in a liquid contact 4 or 5 configured in accordance with another embodiment of the invention. In this intermediate ring 15, the radial projection 20, which serve to center it axially or laterally and face the stationary part 7, are disposed in the region of the ring canal 9, that is, at the edges of the central openings 16. In the ring canal 9 there is also arranged a control ring 21, which is fastened at the stationary part 7 by means of supports 22 in such a manner that it does not appreciably impede the passage of the liquid metal through the ring canal 9. This control ring 21 forms a gap 23 with the radial projections of the intermediate ring 15. The liquid metal flows through the gap 23 to continuously develop the film in the lower partial ring gap 18 with such effect that in case of a radial deviation of the intermediate ring 15 in the direction of decreasing the gap 23 and, correspondingly, of the partial ring gap 17, the supply of liquid metal is retarded and, because of the pressure in the partial ring gap 18 reduced thereby, a restoring force appears, starting from the film in the outer partial ring gap 17 wherein the full pressure prevails. In this way, the radial centering of the intermediate ring 15 is further enhanced.

What is claimed is:

1. In a high-current, liquid-metal contact arrangement for an electrical machine such as an electric unipolar machine utilized as a motor or the like, the contact arrangement including a ringshaped rotatable member; and, a stationary member adjacent the rotatable member, the stationary member being likewise ring-shaped; first and second surfaces formed on the members respectively, said surfaces being mutually adjacent to conjointly define an annular gap therebetween having an approximately uniform thickness about its periphery; the stationary member having an annular canal means therein through which the liquidmetal conductor is pressed into the annular gap between the stationary and rotatable members under pressure to completely fill the gap thereby establishing a good electrical contact between the members; the improvement comprising: an intermediate ring arranged in the annular gap freely floating in the liquid conductor so as to be radially self-centering in said annular gap, said intermediate ring including axial centering means for axially centering said intermediate ring, said ring having a plurality of openings therein located at the mid portion of the lateral dimension thereof and distributed along the circumference of said ring.

2. The improvement of claim 1, said intermediate ring having outer edge-portions facing the stationary member, said axial centering means comprising radial projections extending from said outer edge-portions respectively.

3. The improvement of claim 1, said intermediate ring having a center portion in the region of said canal means, said axial centering means comprising radial projections formed on said intermediate ring at said center portion facing toward the stationary member.

4. The improvement of claim 3 comprising a stationary control ring mounted in the region of said canal means, said control ring and said projections of said intermediate ring conjointly defining a gap therebetween.

5. The improvement of claim 1 comprising at least an additional intermediate ring disposed in said annular gap between the rotatable member and the stationary member. 

1. In a high-current, liquid-metal contact arrangement for an electrical machine such as an electric unipolar machine utilized as a motor or the like, the contact arrangement including a ringshaped rotatable member; and, a stationary member adjacent the rotatable member, the stationary member being likewise ringshaped; first and second surfaces formed on the members respectively, said surfaces being mutually adjacent to conjointly define an annular gap therebetween having an approximately uniform thickness about its periphery; the stationary member having an annular canal means therein through which the liquidmetal conductor is pressed into the annular gap between the stationary and rotatable members under pressure to completely fill the gap thereby establishing a good electrical contact between the members; the improvement comprising: an intermediate ring arranged in the annular gap freely floating in the liquid conductor so as to be radially self-centering in said annular gap, said intermediate ring including axial centering means for axially centering said intermediate ring, said ring having a plurality of openings therein located at the mid portion of the lateral dimension thereof and distributed along the circumference of said ring.
 2. The improvement of claim 1, said intermediate ring having outer edge-portions facing the stationary member, said axial centering means comprising radial projections extending from said outer edge-portions respectively.
 3. The improvement of claim 1, said intermediate ring having a center portion in the region of said canal means, said axial centering means comprising radial projections formed on said intermediate ring at said center portion facing toward the stationary member.
 4. The improvement of claim 3 comprising a stationary control ring mounted in the region of said canal means, said control ring and said projections of said intermediate ring conjointly defining a gap therebetween.
 5. The improvement of claim 1 comprising at least an additional intermediate ring disposed in said annular gap between the rotatable member and the stationary member. 